Multiplex telephony system



Dec. 9, 1941. M. WOLF 2,265,216

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J4. Woff fa mum flTTOR/VEY Patented Dec. 9, 1941 MULTIPLEX TEL PHONY srs'mu Mcnno Wolf, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as

trustee I Application April 20, 1939, Serial No. 269,034

In Germany April 23, 1938 2 Claims. (Cl. 179-15) My invention relates to multiplex telephony systems using cathode-ray tubes for current distribution.

More specifically, my invention is concerned with systems comprising a cathode-ray tube serving as 'a current distributor at the transmitter and having a common anode connected to the transmission line which is common to all channels and each of its electrodes connected to one of the speech channels, and a cathoderay tube serving as a current distributor at the receiver and having a control electrode connected to the transmission line and a plurality of anodes each connected to one of the speech channels. The system also comprises synchronously-acting means for deflecting the cathode-ray beams of the tubes in such a manner that at the transmitter the beam successively passes the control electrodes and is modulated by the voltages applied to these electrodes, and that at the receiver the-beam successively strikes the anodes and successively connects the speech channels to the transmission line.

In known systems of the above type the control electrodes or anodes are usually equally spaced apart on a circular arc, and the deflecting means produce an electric or magnetic rotating field to cause the cathode-ray beam to be successively modulated by the voltages applied to the control electrodes, and at the receiver to cause the beam to successively strike the anodes. Furthermore, the deflecting means are such as to cause the cathode-ray beam to be moved at a uniform speed.

One object oi. my invention is to increase the periods of time available for the transmission of conversation in such systems.

A further object is to decrease cross-talk between the various speech channels.

Further objects and advantages of my invention will appear as the description progresses.

In accordance with the invention 1 provide deflecting means of such a type that the cathoderay beam is displaced in jumps or stepwise from one control electrode or anode to the next control electrode or anode.

In one embodiment of the invention I provide means for deflecting the cathode-ray beam in a single direction and arrange the control electrodes or anodes side by side in the direction of movement of the cathode-ray beam. In this case I prefer to employ deflecting means which produce an electric field or magnetic field whose intensity increases from an initial value in jumps to a final value and then decreases abruptly to the initial value.

By using the invention in systems of the above-described type, the time required for the passage of the cathode-ray beam between successive electrodes or anodes is exceedingly small, and as a result the time available for the transmission of conversation is materially increased and the cross-talk between the various speech channels is reduced.

In order that the invention may be clearly understood and readily carried into eflect, I shall describe the same in more detail with reference to the accompanying drawing, in which,

Fig. 1 is a schematic diagram of a telephony system embodying the invention, and

Fig. 2 is a graph giving a voltage-time curve. The multiplex telephony system illustrated in Figure 1, which serves to transmit four speech channels, comprises a transmitter and a receiver connected by a common transmission line 5. The four channels are connected successively and periodically to the transmission line 5 at both the receiver and transmitter, and for this-purpose the transmitter and receiver are provided with cathode-ray tubes 6 and [6 respectively.

Cathode-ray tube 6 has at one end an electrode system for producing the cathode-ray beam, which system comprises an incandescible cathode I heated from a suitable source (not shown), a cylindrical auxiliary electrode 8, and a first anode 9 connected to a positive potential. At the other end of the tube is a screen In provided with four slit-like apertures 30. Behind each of the apertures 30 is arranged a pair of electrodes ll shown as two electrically-interconnected parallel rods of conductive material. Each pair of the electrodes ii is electrically connected to one of the transmitting channels l---4. Behind electrodes II is. an anode I! which is Y connected to the transmission line 5. Adjacent the first anode 9 is a pair of parallel deflecting plates 13 which are connected to a voltage-producing device l4. Device I4 is adapted to apply across plates l3 a voltage E which varies stepwise with time and has a course as shown in Fig. 2.

As shown in Figure 2, the voltage varies in four steps and the time between these steps is very small and considerably less than the time during which the voltage of each step is applied.

The cathode-ray tube It, which serves to connect the transmission line 5 successively and 55 periodically to each of the receiving lines 3| to 34 comprises at one end an electrode system for producing the cathode-ray beam, which system comprises an incandescible cathode l'l connected to a suitable supply of heating current (not shown), a control electrode l8 connected to transmission line 5, and a first anode l9 connected to a positive potential. Arranged at the other end of the tube on a circular are are four anodes 20 each connected to one of the receiving lines 3| to 34. Adjacent the first anode I9 is a pair of parallel deflecting plates 2| connected to a voltage device 22. Device 22, which may be similar to device l4, serves to produce a voltage E, such as shown in Fig. 2, across plates 2| to thereby deflect the cathode-ray beam, and cause the same to successively strike anodes 20 and move in steps. A generator which produces a deflecting voltage of the shape shown in Fig. 2, and which is suitable for use as the generators l4 or 22 is described in the U. S. Patent #1,955,332.

During operation of the system the cathoderay beam of the tube 8 passes successively through the slit-like apertures 30 and between the corresponding electrodes H upon anode l2. At the same time the beam is modulated by the voltages produced in the lines I to 4 and applied to the control electrodes II, with the result that the so-modulated anode current is transmitted via the transmission line to the receiver. As the voltage applied to the deflecting plates l3 follows the curve shown in Fig. 2, the cathoderay beam successively passes through the apertures 30 and passes through each aperture for a time period indicated by At in Figure 2, during which the anode current is modulated by the voltages produced in the corresponding line |4. At the end of each time period At the cathoderay beam moves in a jump to the next aperture 30, and as this movement takes place in a very short time (1), substantially no time is wasted for the transmission of speech. After the cathode-ray beam has struck anode l2 whilepassing through one of the apertures 30 at the end of the screen, the beam abruptly returns to the aperture 30 at the other end of the screen,

whereupon the beam again passes successively through the apertures.

A current modulated successively by the voltages produced in lines I to 4 is transmitted over the transmission line 5 to the control electrode I 8 of tube "5, with the result that the intensity of the cathode-ray beam of this tube is controlled successively and periodically in accord ance with the voltages produced in lines 1-4.

The cathode-ray beam of tube I6 is given a movement in synchronism with that of the cathode-ray beam of tube 6, so that during the time interval At during which the cathode-ray beam of tube 6 is being modulated, for example by the voltages produced in line I, the cathode-ray beam of tube i6 strikes the anode 20 connected to line 3|. For this purpose the voltage-producing device 22 must be synchronized with device I4. The transmission of the conversations in lines 2, 3 and 4 to the lines 32, 33 and 34 is effected in a similar way.

It is of course necessary that the movement of the cathode-ray beam of tube 6 be in synchronism with that of the cathode-ray beam of tube l6, and in the system illustrated the desired synchronism is obtained in a very simple manner. More particularly, the anode current of tube 6 is suppressed during each time period 1- in which the cathode-ray beam moves from one slit-shaped aperture 30 to the next one, and there is periodic interruption in the oscillations transmitted through transmission line 5 between each two successive jumps of the cathode-ray beam of tube 6. Thus to synchronize the device 22 with the device l4 it is only necessary to obtain these interruptions from the oscillations received via the transmission line 5. For this purpose I connect a filter 23, e. g. an amplitude filter, between the line 5 and device 22, and control the device 22 in known manner with the impulses occurring in the output circuit of this filter. The above-mentioned patent describes a method of controlling such generators by means of synchronizing impulses produced when the stepwise increase of the deflecting voltage takes place.

While I have described my invention in connection with a specific example and with reference to certain constructions, I do not wish to be limited thereto as obvious modifications will occur to a person skilled in the art.

What I claim is:

1. In a multiplex telephony system having a plurality of channels, a cathode-ray tube serving as a current distributor and having a plurality of control electrodes each connected to one channel and a common anode, a transmission line common to all channels and connected to the anode of said tube, and means to deflect the cathode-ray beam of said tube stepwise and to cause the same to successively strike the control electrodes of said tube, said means comprising a device for producing a deflecting field whose intensity increases in steps.

2. In a multiplex telephony system having a plurality of channels, a cathode-ray tube serving as a current distributor and having a plurality of control electrodes arranged side by side in a line and each connected to one channel and a common anode, a transmission line common to all channels and connected to the anode of said tube, and means to deflect the cathode-ray beam of said tube stepwise and to cause the same to successively strike the control electrodes thereof, said means including a device for producing a deflecting field whose intensity increases in steps from an initial value to a predetermined value and then decreases rapidly to the initial value. I

MENNO WOLF. 

